Dye penetrant inspection process

ABSTRACT

Viscous compositions of gel-like consistency are disclosed for removing excess dye penetrant from parts subjected to liquid dye penetrant inspection. The compositions comprise a cleaner, a carrier, and a viscosity increasing agent, and have a viscosity between 10 and 100 poises at 100 reciprocal seconds.

United States Patent [191 Molina Jan. 15, 1974 DYE PENETRANT INSPECTIONPROCESS [75] Inventor: Orlando G. Molina, Westminster,

Calif.

[73] Assignee: Air Products and Chemicals, Inc.,

Allentown, Pa.

[22] Filed: Feb. 25, 1971 [21] 'Appl. No.: 118,979

Related US. Application Data [62] Division of Ser. No. 852,458, Aug. 22,1969,

4/1954 Clarke 73/104 Primary ExaminefRichard C. Queisser AssistantExaminer-John P. Beauchamp Attorney-James C. Simmons [5 7] ABSTRACTViscous compositions of gel-like consistency are disclosed for removingexcess dye penetrant from parts subjected to liquid dye penetrantinspection. The compositions comprise a cleaner, a carrier, and aviscosity increasing agent, and have a viscosity between 10 and 100poises at 100 reciprocal seconds.

1 Claim, N0 Drawings Alburger 73/104 DYE PENETRANT INSPECTION PROCESSThis is a division of application Ser. No. 852,458, filed Aug. 22, 1969,now abandoned.

BACKGROUND OF THE INVENTION The process of dye penetrant inspection is awellknown non-destructive inspection technique. Broadly, it comprisesthree steps. The first step is the application of liquid dye penetrantto the part to be inspected either by dipping, brushing or spraying. Thedye penetrant, in addition to coating the surface of the part,penetrates any cracks, surface flaws or fissures in the part. The secondstep is the removal of excessdye penetrant by superficially cleaning thesurface of the part, allowing residual dye penetrant to remain in anycracks or defects which exist in the stated surface. The third step isthe developing of the dye penetrant by application of a developercoating to cause the mentioned residual dye penetrant remaining insurface defects to form a visible pattern or trace in the statedcoating. Where the dye penetrant is clearly visible without anydeveloper, the foregoing third step is omitted.

The removers used in the prior art to accomplish the process of thesecond step above are mobile liquids. Mobile liquid dye penetrantremovers have several disadvantages. In general, the amount of dyepenetrant removed is a function of the time that the remover is on thepart. The remover must consequently be used with great skill and care orit will remove the residual dye penetrant in the flaws of the part, inaddition to the undesirable dye penetrant on the surface of the part,resulting in a total absence of any dye trace in the developer coating.Additionally, if a large surface is not planar and horizontal, run-offof remover will cause uneven removal of dye penetrant. An additionaldisadvantage ofa mobile liquid remover is apparent when parts, whetherlarge or small, must be coated on their underside, due to a fixedlocation in an assembly. In such a fixed location, remover drips fromthe part, making the process inconvenient, messy and imprecise.

SUMMARY OF THE INVENTION The objects of this invention are accomplishedby the use of a novel one-phase viscous dye penetrant remover. Theone-phase viscous dye penetrant removers of the instant inventioncomprise a dye penetrant cleaner, a viscosity increasing agent, and acarrier. These removers have an apparent viscosity between and 100poises at 100 reciprocal seconds. The preferred remover comprises water,a nonionic detergent, and water soluble pine oil.

DESCRIPTION OF THE PREFERRED EMBODIMENT Dye penetrants with ketone,hydrocarbon, glycol or chlorinated hydrocarbon bases have provedsuccessful in the prior art. However, dye penetrants based upon acetone,benzene, or other solvents, both oil based and spirit type, are known tobe feasible. Water is generally not suitable for a dye penetrant base,as its high surface tension renders it unsuitable for penetration ofnarrow or microscopic cracks. Whatever base dye penetrant is chosen, theremover must naturally be one which will remove the excess dyepenetrant. The critical requirements of the dye penetrant cleanercontemplated in this case are that the cleaner must be capable ofremoving the dye penetrant, either by dissolution or emulsification,that it be miscible with the rest of the remover system, and that it becompatible with a highly viscous system. The particular agent chosenwould be selected with the characteristics of the dye penetrant and therest of the remover system in mind.

Cleaners found suitable for use in the instant invention have includedwater dispersible pine oil, methyl ethyl ketone and gasoline. These havebeen found effective in the removal of dye penetrants comprising organicdyes and methyl chloroform and penetrants comprising organic dyes andmethyl isobutyl ketone, or oily and oil-like vehicles.

The viscosity increasing agents of the instant invention can be of sucha nature that the remover becomes a highly viscous liquid, or such thatthe remover becomes a gel. For the purposes of this specification, a gelis a semi-liquid which has a definitely ascertainable yield shearstrength. Whether the remover is a gel or a liquid, it should have aviscosity large enough such that when the viscous remover is applied tothe part to be inspected, the remover will not flow into cracks,fissures, and flaws in the part. That is, the remover will contact onlysurface or excess dye penetrant and will not penetrate defects so as toremove dye in defects in the part. Naturally, the viscosity levelrequired to avoid penetration of defects in a part "depends upon thewidth of the defect. For weld inspection purposes, wherecracks as smallas 5 microns in width must be detected, a minimum apparent viscosity of10 poise is suitable..lt can be seen that the upper limit of viscosityis set by the simple consideration of ease of application. With ease ofapplication being the principal criteria for the upper limit ofviscosity, quite high viscosities, for instance, poise or even higherare suitable.

The viscosity increasing agent of this invention must meet some of thesame requirements that the cleaner satisfies. The viscosity increasingagent must be compatible with the remover system such that a homogeneousliquid or gel is formed. Accordingly, the nature of the dye penetrant,cleaner and carrier must be kept in mind when specifying a suitableviscosity increasing agent. For instance, in a system using methylisobutyl ketone based dye, pine oil cleaner, and water carrier, 3nonionic detergent such as Tergitol NPX, sold by Union Carbide, is asuitable viscosity increasing agent, producing a gelled dye penetrantremover. For other systems, other viscosity increasing agents would bemore suitable. For example, pyrogenic silica, cellulose ether, soaps,fine particle alumina, gums and soluble high molecular weight polymersare viscosity increasing agents known in the prior art. The exactcomposition of the viscosity increasing agent is not critical; itsnature is. Any composition would be suitable, as long as it iscompatible with the rest of the remover system and increases theviscosity of the system. Tergitol nonionic NPX is a nonyl phenylpolyethylene glycol ether containing 10.5 mols of ethylene oxide andhaving the general formula C H1 O(CH O) 10.5H.

The third component of the novel dye penetrant remover of the instantinvention is a carrier. Water is the most common carrier, being the mostinexpensive. The carrier, like the cleaner and the viscosity increasingagent, must be selected with the nature of the dye penetrant and therest of the remover system in mind. It has been found that the mosteconomical systems are based upon water, although a suitable system maycomprise, for instance, alcohol as a carrier, a viscosity increasingagent capable of gelling alcohol, for instance, pyrogenic silica, and acleaning agent, such as methyl isobutyl ketone. This system would besuitable for removing excess dye penetrant that is soluble in alcohol.It will be noted that ungelled alcohol would remove all the dyepenetrant from most surface defects, including very narrow flaws andwould be unsuitable according to the teachings of this invention becauseof this excessive cleaning effect.

The primary requirements for a carrier to be used in the instantinvention is that the carrier be miscible and compatible with theviscosity increasing agent and cleaner. As indicated previously, a watercarrier is preferred, but it is also to be understood that othercarriers are within the scope of the instant invention. Such carriersinclude alcohol, chlorinated hydrocarbons, benzene and gasoline.

Although the three major components of the dye penetrant remover of theinstant invention have been designated as carrier, cleaner and viscosityincreasing agent, each can, to some degree, perform the function of theother. For instance, in a system comprising pine oil, nonionic detergentand water, the water is nominally the carrier; the detergent, theviscosity increasing agent; and the pine oil, the cleaning agent.However, it should be noted that in this system the nonionic detergentalso performs a cleaning function in addition to its nominal viscosityincreasing function. Accordingly, a system can be formulated that onlyhas two components, one of the two components serving two functions. Anexample of such a system would be methanol and Klucel, a tradename for acellulose ether produced and sold by Hercules Powder Co. In this system,the methanol would act as both a carrier and a cleaner. The preferredremover system, suitable for most dye penetrants, comprises from 1 to 2parts by weight water soluble pine oil, from 1 to 2 parts by weightnonionic detergent and from 1 to 8 parts by weight water. Pine oil, asunderstood by those skilled in the art, includes terpene alcohols ortheir derivatives, principally isomeric tertiary and secondary cyclicterpene alcohols, ketones and ethers with relatively high boilingterpene hydrocarbons.

Once the improved remover is formulated, its use is similar to that ofprior art removers. The part to be inspected is coated with dyepenetrant, and the dye penetrant is allowed to penetrate. For rapidityof inspection, dye penetrants based on volatile solvents are preferred.After the dye penetrant has penetrated, the viscous remover of theinstant invention is applied to the part. It is at this point that theremovers improvement on the prior art becomes manifest. The remover neednot be immediately removed. Since the viscous remover does not penetratethe flaws, there is no chance of the dye therein being removed. At somelater time, then, the remover is cleaned off the part, and the dyeremaining in the flaws is developed. An additional advantageous featureof the compositions of the instant invention is a novel variablesensitivity. The system can be so designed that additional carrier canbe added, making the remover less sensitive. It should be noted that theaddition of carrier will make the remover less viscous. This will enablethe remover to penetrate flaws previously inaccessible. This effect isgenerally outweighed by the decreased strength of the remover due to thefurther diluting of the cleaner.

The following examples illustrate the composition of the instantinvention; all compositions are given in parts by weight.

EXAMPLE I A dye penetrant remover was formulated of 3 parts water, 1part of Tergitol NPX, described above and designating a nonionicdetergent made and sold commercially by Union Carbide Corp., and 1 partof water soluble pine oil. Water soluble pine oil is a commerciallyavailable formulation that comprises pine oil and a nonionic detergentso formulated that the pine oil composition will emulsify very readilyin water.

The remover, a gel, was applied to a flawed weldment that had previouslybeen treated with a chlorinated hydrocarbon based dye penetrant. Afterthree minutes, the remover and surface dye penetrant was washed off withwater. A developer was then applied, revealing flaws in the weldment.

EXAMPLE II A remover formulation identical to that of Example I wasapplied to a dyed weldment similar to that of Example l. The remover wasallowed to stand for 72 hours, and then washed off with water.Application of developer revealed the same size and type of flaws in theweldment as were detected in Example 1.

EXAMPLE III A remover composition was formulated using 8 parts of water,1 part of Triton X-l55, a tradename for a nonionic detergent sold byRohm and Haas, and 1 part of water soluble pine oil. This less viscousremover composition was applied to a dyed defective weldment of the typeused in Example I. After 5 minutes, the composition was washed away withwater. More flaws were evident than in the previous two examples,indicating an increased sensitivity in the less viscous remover.

EXAMPLE IV A remover composition was formulated using 98 parts ofmethanol, and 2 parts of Klucel. This composition was used to removedried dye penetrant from the surface of a defective weldment. Theremover was then wiped off the part. Subsequent development revealedflaws in the weldment. It will be noted that the methanol acted as boththe cleaner and the carrier.

EXAMPLE V A remover composition was formulated using parts of acetoneand 5 parts of Cab-O-Sil N5, a tradename for pyrogenic silica producedand sold by Cabot Corp. This gelled composition was used to remove drieddye penetrant from the surface of a deflective weldment. The remover wasthen wiped off the part. Subsequent development revealed flaws in theweldment. It will be noted that the acetone acts as both the cleaner andthe carrier.

I claim:

1. A method of maximizing the number of visual indications in a dyepenetrant nondestructive inspection process for surface discontinuitiesin a specimen comprising the steps of:

applying to said surface a liquid dye penetrant adapted to enter saiddiscontinuities;

cess penetrant from said surface while said dye penetrant remains insaid discontinuities; and applying a developer to the surface of thespecimen to reveal the type and location of the surface discontinuities.

